Mobility and broadband has become development orientations of modern communication, and the 3rd Generation Partnership Project is making an effort to develop a Long Term Evolution (LTE) system as an evolved 3G system for the purpose of evolving a 3GPP radio access oriented toward high data rate, low delay and optimized packet data applications. The multi-antenna technology at the physical layer has become one of crucial technologies for an existing mobile communication system and offers numerous advantages, e.g., a throughput of the system improved due to a multiplexing gain of multiple antennas, the performance of the system improved due to a diversity gain of multiple antennas, interference between users eliminated by distinguishing one user from another due to a directional gain of the antennas, etc.
At present, the design of the LTE system has been substantially completed in the standardization effort of the 3GPP, and frame structures for a general transmission scheme of the LTE system in an FDD system and a TDD system are as illustrated respectively in FIG. 1 and FIG. 2. Downlink signaling and downlink data, and uplink signaling and uplink data as well their mutual transmission relationships are defined for each operating carrier, where two ends of a frequency band are occupied for uplink control signaling transmitted through frequency-hopping, that is, different frequency ranges will be occupied for transmission of the uplink control signaling in two time slots of a sub-frame.
The uplink control signaling is subject to orthogonal sequence spreading and then mapped into an uplink control channel for transmission, thus a plurality of uplink control channels can be transmitted concurrently on the same Physical Resource Block (PRB). Each uplink control channel corresponds to a unique orthogonal sequence number, and a UE can determine from the orthogonal sequence number an orthogonal spreading sequence for its corresponding uplink control channel and the location of the PRB where the uplink control channel is located.
At present there are two different formats of an uplink control channel, i.e., the format 1/1a/1b and the format 2/2a/2b. ACK/NACK information corresponding to a downlink data packet and an uplink Scheduling Request (SR) is carried in the format 1/1a/1b. Channel quality related information, e.g., a Channel Quality Information (CQI), a Pre-coding Matrix Information (PMI), a Rank Information (RI), etc., is fed back in the format 2/2a/2b.
For a dynamically scheduled downlink data packet, the number of an uplink channel on which ACK/NACK information is fed back (i.e., a orthogonal sequence number) will be derived from the number of a Control Channel Element (CCE) occupied for a downlink control channel on which scheduling information of the data packet is carried, that is, a unique uplink channel resource number can be derived from a CCE number. In an LTE Rel-8 system, a UE will transmit only one uplink control channel at most in each sub-frame due to an uplink limitation arising from uni-carrier transmission, thus an uplink control channel in actual use is an uplink control channel corresponding to a first CCE occupied for a downlink control channel serving the UE.
ACK/NACK corresponding to a persistently scheduled downlink data packet, an SR and a CQI/PMI/RI transmitted in the format 2/2a/2b are fed back periodically, and a base station can know in advance specific temporal locations at which the respective information is transmitted, thus the numbers of channels on which the foregoing control signaling is transmitted are allocated in advance by RRC signaling from the base station to a UE.
In the ongoing study of an uplink control channel for a Long Term Evolution-Advanced system, a possibility has been proposed to use Orthogonal Resource Transmit Diversity (ORTD) for transmit diversity in transmission of an uplink control channel for a UE configured with a plurality of transmission antennas to thereby improve the reliability or capacity of transmitting uplink control signaling. As ORTD implies, each antenna port corresponds to one orthogonal sequence, and the same information is spread in different orthogonal sequences and then transmitted concurrently by different antenna ports. A receiver extracts signals from the different antenna ports and then combines them for detection to thereby achieve a diversity gain.
FIG. 3 illustrates a schematic diagram of transmit diversity through ORTD with two antennas, where Tx0 and Tx1 represents two transmission antenna, n_r0 and n_r1 represent two orthogonal sequence numbers different from each other, and s represents feedback information. A study shows an insignificant performance gain of ORTD with four antennas as compared with that with two antennas. In view of an overhead of an orthogonal sequence and alike, a hybrid scheme of ORTD and virtual antennas as illustrated in FIG. 4 is recommended for four antennas. As compared with the ORTD-only scheme, a process of virtualizing antennas is added here for transmission of information of two antenna ports on four physical antennas, and this virtualizing process is transparent to a base station, that is, the base station can receive without any knowledge of whether a transmitter transmits on two or four antennas.
Dependent upon a specific transmission condition and demand, a UE configured with a plurality of transmission antennas can alternatively go back to a single antenna port transmission mode which can be performed in the following two approaches:
A first approach is transmission on a single physical antenna as illustrated in FIG. 5, which is the same as that in the LTE Rel-8 system.
A second approach is concurrent transmission of the same information with the same orthogonal sequence to thereby improve actual transmit power and hence the reliability of transmission, a schematic diagram of which is as illustrated in FIG. 6.
Transmission in the first or second approach is transparent to a receiver, that is, the receiver can receive and demodulate without any knowledge of which transmission approach is particularly used.
However there is no method for configuring transmission of an uplink control channel in a plurality of transmission modes for a high-level UE configured with a plurality of transmission antennas, making it impossible to make full use of the advantages of the UE being provided with a plurality of transmission antennas, thus it is necessary to propose a corresponding technical solution in which a base station configures flexibly the UE configured with a plurality of transmission antennas dependent upon an operating status of a system to have the UE transmit an uplink control channel in a varying mode.